The patterns of output activity generated by motoneurons results from the interplay of intrinsic and extrinsic factors. Among the intrinsic factors are the size, morphology, and membrane characteristics of motoneurons; extrinsic factors are the types and patterns of pre-motor interneuronal activity. The spiracle control system in cockroaches of the genus Blaberus offer a unique opportunity to explore the roles played by these factors in shaping the pattern of motoneurone output. Two types of abdominal spiracle are found in Blaberus discoidalis, one type exclusively respiratory and the other defensive. Movements of each spiracle, whether respiratory or defensive, are controlled by three motoneurones. The activity patterns of these serially homologous sets of motoneurones are not identical, but vary with the function of the spiracle. The activity patterns of motoneurones innervating respiratory and defensive spiracles have been thoroughly characterized in intace animals. The aim of this research program is to determine the roles of intrinsic and extrinsic factors in determining the output patterns of these functionally specialized serially homologous sets of motoneurones. Intracellular cobalt staining will be used to reveal the morphology of spiracular motoneurones. The morphology of these cells will be compared and attempts will be made to correlate morphology and function. Intracellular recordings will be made from spiracular motoneurones to determine if different functional types receive similar synaptic inputs. The responses of these motoneurones to imposed deplorizations and hyperpolarizations and to release from hyperpolarization will be compared. Similar morphological and electrophysiological data will be collected from interneurones pre-synaptic to spiracular motoneurones. BIBLIOGRAPHIC REFERENCES: Pearson, K.G., R.K. Wong and C.R. Fourtner (1976) Connection between hair plate afferents and motoneurons in the cockroach legs. J. Exp. Biol. 64, 251-266. Drewes, C.D. and C.R. Fourtner (1976) Stretch sensitive neural units in the body wall of the earthworm. J. Exp. Biol. 65, 39-50.